Liquid crystal display viewable under all lighting conditions

ABSTRACT

A liquid crystal display (LCD) viewable under all lighting conditions without excessive power consumption is described. The LCD comprises a first dichroic polarizer, a second dichroic polarizer, an anti-reflection layer positioned in front of the first dichroic polarizer and a liquid crystal cell positioned between the first dichroic polarizer and the second dichroic polarizer. In addition, the LCD comprises a backlight assembly positioned behind the second dichroic polarizer. Finally, the LCD comprises a diffusing transflector positioned between the backlight assembly and the second dichroic polarizer. The diffusing transflector comprises a diffusing element and a transflective element.

This application is a divisional of copending application Ser. No.10/370,360 filed on Feb. 18, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a liquid crystal display device, and moreparticularly, to an improved transflective liquid crystal displayviewable under all lighting conditions, such as total dark, indoorlighting, in shade, medium sunlight, strong sunlight, and directsunlight, without excessive power consumption.

2. Description of the Related Art

Many features of liquid crystal displays (LCDs), such as light weightand size, low power consumption and high resolution, make LCDs a popularchoice in various electronic applications. These applications includedigital cameras, palm PCs, notebook computers, tablet PCs, workstations,and navigation systems in automobiles, marine vessels, and airplanes.Most of these applications are portable and can be transited betweenindoor and outdoor. Thus, there is a need to develop a display toaccommodate both indoor and outdoor environments and perform regardlessof different lighting conditions. Various types of LCDs have evolvedaround this need.

With reference to FIG. 1, a conventional transmissive liquid crystaldisplay (LCD) is shown. The LCD includes a liquid crystal cell 100comprising a front transparent electrode with color filters 101, a reartransparent electrode (pixel portions) 102, and a layer of liquidcrystals 103 between the front and rear transparent electrodes. Theliquid crystal cell 100 is usually sandwiched by a front glass substrate104 and a rear glass substrate 105. A first dichroic polarizer 106adheres to the front surface of the front glass 104. Likewise, a reardichroic polarizer 107 adheres to the rear surface of the rear glass105. The transmissive display further includes a backlight cell assembly108. A regular LCD contains 1 to 4 lamps that provide between 100 and300 nits of illumination 110 at the surface of LCD. This level ofbrightness enables this type of LCD to perform beautifully indoors. Inan outdoor setting, the anti-glare surface of the first polarizer 106reflects and diffuses about 3% to 5% of the ambient sunlight A to aviewer's eyes. The amount of background reflection 109 is strong,overwhelming the illumination 110 from the backlight 108 and obscuringthe image generated by the LCD.

One approach used to improve the performance of this type of LCD undersunlight is to apply an anti-reflection coating on the front surface.Although providing some improvement, the anti-reflection coating aloneis not sufficient to provide an LCD viewable under direct sunlight.Further improvement is necessary.

Another solution commonly adopted is to increase the illumination oftransmissive LCDs for outdoor application by adding more lamps to thebacklight cell. The term “high-bright LCD” describes this modifiedtransmissive LCD. In general, an LCD requires at least 1000 nits ofillumination to be viewable under sunlight. To reach this level ofbrightness, an LCD requires 10 to 12 lamps. The additional lamps consumemore power, generate excessive heat, experience contrast washout andrequire dimension and circuit alterations. Alterations of the LCD'sdimensions and circuits are costly. Thus, high bright LCDs generallycreate more problems than they solve.

Referring now to FIG. 2, a common construction of a reflective LCD isshown. A reflective LCD does not have problems with power consumptionsince ambient light A is used for illumination. A reflector 201 ispositioned behind a liquid crystal display assembly 204. Generally, thereflector 201 is an opaque surface of highly reflective material (suchas aluminum or silver) with 90% to 98% reflection. The LCD displayassembly 204 may also contain a second dichroic polarizer (not shown). Aportion of ambient light 202 passes the liquid crystal display assemblyand reaches the reflective surface of reflector 201. The reflector 201reflects ambient light portion 202 and uses it as the display'sillumination 203. Because the display's illumination is tied to theamount of ambient light provided, the visibility of reflective LCD ishighly surrounding-sensitive. Under strong ambient light, the LCD hasgood illumination. However, LCD brightness diminishes as ambient lightdecreases. This disadvantage of the reflective LCD strongly limits itsapplications.

With reference to FIGS. 3A and 3B, a “transflective LCD” is shown. Thetransflective LCD was developed to overcome the shortcomings of thereflective LCD. A major element of the transflective LCD is the“transflector”, which is partially transmissive and partiallyreflective. The transflector uses ambient light and/or a backlight toilluminate the LCD. One type of transflective LCD implements thetransflector as a series of electrodes 301, where the electrodes 301 areimbedded within the compartment of pixel portions 102 of the liquidcrystal cell 100. FIG. 3A shows the structure of a transflective LCDwith transflective electrodes 301. In FIG. 3B, the cropped partial areaof the pixel portions 102 with transflective electrodes 301 is shown.The transflective electrodes 301 have highly reflective regions 301 rand transmissive portions 301 t contacting the transparent electrodes ofpixel portions 102. When ambient light A is not strong, the transmissiveportions 301 t allow the transmission of light B from backlight cell 108as the illumination 302 of LCD. When ambient light A is strong, thereflective portions 301 r reflect ambient light 303 entering the liquidcrystal panel 100, and send it back out as illumination 304 of LCD.

Still referring to FIGS. 3A and 3B, the visibility of the LCD isexcellent when the ambient light A is strong. However, the combinationof reflective portions 301 r and transmissive portions 301 t within thesame domain (pixel portions 102) imposes undesirable features on theLCD. The problems are more noticeable when the LCD is used indoors, andinclude low brightness, loss of color, low contrast and a narrow viewingangle. In addition, pixel size of the LCD is limited by the need toaccommodate both transmissive and reflective electrodes. The limitedpixel size results in increased manufacturing difficulties and costs forhigher resolutions.

Another type of transflective LCD comprises a transflective plastic filmas the transflector, positioned in the rear of liquid crystal panel (notshown). Although easy to construct, this type of transflective LCD hasinefficient illumination. The commonly used transflective films normallyhave 20% to 40% transmission efficiency and 50% to 70% reflectionefficiency. Thus, this type of transflective LCD is not as bright aseither purely reflective or purely transmissive LCD types.

In summary, a regular liquid crystal display can have satisfactoryperformance either indoors or outdoors. A high bright LCD, thoughacceptable for both indoor and outdoor applications, consumes high powerand demands various complimentary re-designs of the device system toaccommodate the excessive heat. Reflective LCDs do not perform wellindoors. Transflective LCDs are limited by pixel size and do not performoptimally under certain ambient light. Thus, there is a great need todevelop a liquid crystal display assembly that consumes low powerwithout excessive heat generation, and has good color, adequatebrightness and sufficient contrast under all lighting conditions.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a liquid crystaldisplay with good color, adequate brightness and sufficient contrast foroutdoor applications.

A second object of the invention is to provide a liquid crystal displaywith good color, adequate brightness and sufficient contrast for indoorapplications.

A third object of the invention is to provide a liquid crystal displaythat is viewable in direct sunlight with no alteration of the viewingangle.

A fourth object of the invention is to provide a liquid crystal displaythat is viewable under direct sunlight and does not consume high powerto cause excessive heat generation.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a liquid crystal display viewable under all lightingconditions without excessive power consumption. The LCD comprises afirst dichroic polarizer, a second dichroic polarizer, ananti-reflection layer positioned in front of the first dichroicpolarizer and a liquid crystal panel positioned between the firstdichroic polarizer and the second dichroic polarizer. In addition, theLCD comprises a backlight assembly positioned behind the second dichroicpolarizer. Finally, the LCD comprises a diffusing transflectorpositioned between the backlight assembly and the second dichroicpolarizer. The diffusing transflector comprises a selective diffusingelement and a selective transflective element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 is a diagram of the structure of a conventional transmissiveliquid crystal display (related art).

FIG. 2 is a diagram of a common structure of a reflective LCD (relatedart).

FIG. 3 a is a diagram of the structure of a transflective LCD withtransflective electrodes (related art).

FIG. 3 b is a diagram of an enlarged cropped section of the pixelportions containing the transflective electrodes of FIG. 3 a (relatedart).

FIG. 4 is a diagram of one embodiment of the present invention.

FIG. 5 is a diagram of the spectrum measurements of a selectivereflective polarizer in the visible region.

FIG. 6 is a diagram of the propagations of the reflective lights throughthe diffusing transflector.

FIG. 7 is a diagram of an alternative embodiment of the presentinvention.

FIG. 8 is a diagram of the structure of a 15″ desktop monitor TFT LCD(related art).

FIG. 9 is a diagram of an embodiment of the present invention modifyinga 15″ desktop monitor TFT LCD.

FIG. 10 is a diagram of a comparison of temperature measurements betweenthe monitor of FIG. 8 and the monitor of FIG. 9.

FIG. 11 is a diagram of the structure of a 14.2″ notebook computer TFTLCD (related art).

FIG. 12 is a diagram of an embodiment of the present invention modifyinga 14.2″ notebook computer TFT LCD.

FIG. 13 is a diagram of the structure of a 10.4″ Tablet TFT LCD (relatedart).

FIG. 14 is a diagram of an embodiment of the present invention modifyinga 10.4″ Tablet TFT LCD.

FIG. 15 is a diagram of the structure of a 12.1″ open frame high brightTFT LCD (related art).

FIG. 16 is a diagram of an embodiment of the present invention modifyinga 12.1″ open frame high bright TFT LCD.

FIG. 17 is a diagram of the structure of a 1.5″ TFT LCD (related art).

FIG. 18 is a diagram of an embodiment of the present invention modifyinga 1.5″ TFT LCD.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 4, an illustration of one embodiment of thepresent invention is shown. Transflective LCD 400 includes aconventional liquid crystal display panel 409. The transflective LCD 400also includes a low reflection first polarizer 410. The rear side of lowreflection first polarizer 410 is bonded to the front side of LCD panel409 using optical bonding material. The low reflection first polarizer410 is composed of an anti-reflection (AR) layer 401 and a dichroicpolarizer 402. The anti-reflection layer 401 can be a high efficiencymulti-layer anti-reflection coating applied directly on the frontsurface of the dichroic polarizer 402. The anti-reflection layer 401 canalso be a separate transmissive substrate, glass or plastic, with an ARcoating on the front side. The rear side of the transmissive substrateis bonded to the front side of dichroic polarizer 402 with anindex-matched optical bonding material to lower the reflection. The lowreflection front surface 401 preferably is a low haze surface (less than15% haze, haze being the surface scattering luminescence over theluminescence of an object) with high efficient multi-layer AR coating,which provides an anti-reflection surface with reflection less than 1%.The low reflection front surface 401 produces less background reflection415 than the regular LCD front surface 106 described in FIG. 1 (by 5 to8 folds). In addition, the low reflection surface 401 allows moreefficient transmission of ambient light A and provides a stronger lightbeam 406 to be used as the reflective illumination 408. Thetransflective LCD 400 also includes a second dichroic polarizer 403optically bonded to the rear of liquid crystal panel 409. In thisembodiment, the transmission directions of the two dichroic polarizers402 and 403 are preferably in parallel. Such an arrangement of 402 and403 provides a transflective LCD that is direct sunlight readablewithout backlight. However, the transmission directions of 402 and 403can also vary from 0 to 90 degrees. It is also preferred that AR coatingis applied to the rear surface of the second dichroic polarizer 403 (notshown). The AR coating maximizes entry of light beam 406 for reflectiveillumination.

Still referring to FIG. 4, the transflective LCD 400 further comprises adiffusing transflector 411 positioned to the rear side of seconddichroic polarizer 403. The diffusing transflector 411 comprises adiffusing element 404 and a selected reflective polarizer 405. Thereflective polarizer 405 preferably has absorption of incident energyless than 10%. The reflective polarizer also has an extinctioncoefficient, defined as the transmission of p state polarization overthe transmission of s state polarization, ranging from 1.5 to 9. Inaddition, the transmission axis of the reflective polarizer 405 isparallel to or within (+/−) 60 degrees of the transmission direction ofthe second dichroic polarizer 403. Reflective polarizer 405 can beformed with multiple sheets of a selective reflective polarizer withoptimized transmission directions. Reflective polarizer 405 can also bea diffuser laminated selective reflective polarizer, which has improvedmechanical and thermal properties.

With reference to FIG. 4, the diffusing element 404 also has acorrugated diffusing surface with haze in the range of 10% to 85%. Thecorrugated surface can be a roughened surface on a transmissivepolymeric substrate, such as PEN (polyethylene naphthalate), PC(polycarbonate), or PET (polyethylene erephthalate). The corrugatedsurface also can be a dielectric material, such as TiO2 (Titaniumdioxide), Ta2O5(Tantalum oxide), SiO2 (Silicon dioxide), SiN (Siliconnitride), ITO (Indium tin oxide), ZnS (Zinc sulphide), Al2O3 (Aluminumoxide), LaF3 (Lanthanum fluoride), MgF2 (Magnesium fluoride), Ge(Germanium) or Si (Silicon) deposited on a transmissive substrate. Thecorrugated surface can further be small metal particles, ranging in sizefrom 10 nm to 10000 nm, deposited directly on the rear side of thesecond polarizer or on a separate transmissive substrate. Choices ofmetal include silver, gold, aluminum, copper, titanium, tantalum,chromium, nickel or an alloy thereof. One or more sheets of lose-packedor optically bonded transmissive substrate with the corrugated surfacecan make up the diffusing element 404. In addition, diffusing element404 can be optically bonded to the rear surface of the second dichroicpolarizer 403 and to the front surface of the reflective polarizer 405.

Still referring to FIG. 4, the transflective LCD 400 further includes ahigh efficiency backlight cell assembly 420. Backlight assembly 420preferably contains one or two orthogonal sheets of brightnessenhancement films and other multiple polymeric films for enhancingtransmission and optical performances. However, any conventionalbacklight cell or high bright backlight cell with edge lamps or backsidelamps can be used.

With reference to FIG. 4, the transflective LCD 400 has a maximizedtransmission 407 with backlight transmitted by a recovery effect fromthe reflective polarizer 405 and the backlight cell 420. Thistransmission illumination coupled with the incorporation of the lowreflection front surface 401 creates good optical performance for allindoor and some outdoor conditions, such as outdoor in shade. Inaddition, diffusing transflector 411 optimizes the total reflectiveillumination 408. A diffusing element with a corrugated surface torandomize light input further optimizes the reflection efficiency of thetransflector, thus providing sufficient reflective illumination.

Referring now to FIG. 5, a diagram of the spectrum measurements of aselective reflective polarizer in the visible region is shown. Thediagram displays the extinction coefficients (the transmission of pstate polarization over the transmission of s state polarization) fordifferent wavelength values. The average extinction coefficient is 3, or75% over 25%.

With reference to FIG. 6, a diagram of the propagations of thereflective lights through the diffusing transflector is shown. The light406 entering the LCD consists mainly of transmissive p polarization 601and also has s polarization 602. The p polarization and s polarizationcomponents are slightly randomized when they pass the diffusing element404. The p polarization 601 yields mainly p polarization 601 t and alsohas s polarization 603. When 601 t reaches the reflective surface 405(with extinction coefficient 3.0), approximately 25% reflects asreflective illumination 601 tR. When s polarization 603 reaches thereflective surface of 405, approximately 75% reflects as reflectiveillumination 603R. By the similar propagation mechanisms, reflectiveilluminations 602 tR and 602R are produced by s polarization 602. Thetransmissions of the reflected beams 604, 605, 606, and 607, additivelygenerate the total reflective illumination 408. Under a very strongambient light, the reflective illumination 408 is sufficient to overcomethe front surface background reflection 415 (FIG. 4), and to facilitatethe viewing of the images under the most challenging conditions.

Referring now to FIG. 7, an illustration of an alternative embodiment ofthe present invention is shown. The transflective LCD 700 comprises aconventional liquid crystal display panel 409. The transflective LCD 700further comprises a low reflection first polarizer 410. The rear side oflow reflection first polarizer 410 is bonded to the front side of LCDpanel 409 using optical bonding material. The low reflection firstpolarizer 410 is composed of an anti-reflection (AR) layer 401 and adichroic polarizer 402. The anti-reflection layer 401 can be a highefficiency multi-layer anti-reflection coating applied directly on thefront surface of the dichroic polarizer 402. The anti-reflection layer401 can also be a separate transmissive substrate, glass or plastic,with an AR coating on the front side. The rear side of the transmissivesubstrate is bonded to the front side of dichroic polarizer 402 with anindex-matched optical bonding material to lower the reflection. The lowreflection front surface 401 preferably is a low haze surface (less than15% haze) with high efficient multi-layer AR coating, which provides ananti-reflection efficiency of less than 1%. The low reflection frontsurface 401 produces less background reflection 415 than the regular LCDfront surface 106 described in FIG. 1 (by 5 to 8 folds). In addition,the low reflection surface 401 allows more efficient transmission ofambient light A and provides a stronger light beam 406 to be used as thereflective illumination 408. The transflective LCD 700 also includes asecond dichroic polarizer 403 optically bonded to the rear of liquidcrystal panel 409. In this embodiment, the transmission directions ofthe two dichroic polarizers 402 and 403 are preferably in parallel. Suchan arrangement of 402 and 403 provides a transflective LCD that isdirect sunlight readable without backlight. However, the transmissiondirections of 402 and 403 can also vary from 0 to 90 degrees. It is alsopreferred that AR coating is applied to the rear surface of the reardichroic polarizer 403 (not shown). The AR coating maximizes entry oflight beam 406 for reflective illumination.

Still referring to FIG. 7, the transflective LCD 700 further comprises adiffusing transflector 711 positioned to the rear side of seconddichroic polarizer 403. The diffusing transflector 711 is composed of adiffusing element 404 and a selective beam splitter 705. Thetransmission of the beam splitter 705 ranges from 30% to 85%. It ispreferred the beam splitter 705 is a multi-layer coating of dielectricmaterial directly deposited to the rear surface of the diffusing element404. However, the beam splitter 705 can also be a multi-layer dielectriccoating deposited on the front surface of a transmissive substrate. Thecoated transmissive separate substrate is positioned on the rear side ofdiffusing element 404.

With reference to FIG. 7, the diffusing element 404 preferably has acorrugated surface with haze in the range of 10% to 85%. The corrugatedsurface can be a roughened surface on a transmissive polymericsubstrate, such as PEN (polyethylene naphthalate), PC (polycarbonate),or PET (polyethylene erephthalate). The corrugated surface also can be adielectric material, such as TiO2 (Titanium dioxide), Ta2O5 (Tantalumoxide), SiO2 (Silicon dioxide), SiN (Silicon nitride), ITO (Indium tinoxide), ZnS (Zinc sulphide), Al2O3 (Aluminum oxide), LaF3 (Lanthanumfluoride), MgF2 (Magnesium fluoride), Ge (Germanium) or Si (Silicon)deposited on a transmissive substrate. The corrugated surface canfurther be small metal particles, ranging in size from 10 nm to 10000nm, deposited directly on the rear side of the second polarizer or on aseparate transmissive substrate. Choices of metal include silver, gold,aluminum, copper, titanium, tantalum, chromium, nickel or an alloythereof. One or more sheets of lose-packed or optically bondedtransmissive substrate with the corrugated surface can make up thediffusing element 404. Diffusing element 404 can be optically bonded tothe front surface of the beam splitter 705, provided the beam splitter705 is a separate substrate, as described above, to form the diffusingtransflector 711, which can be optically bonded to the rear side of thesecond dichroic polarizer 403, as shown, or the front side of the seconddichroic polarizer 403, not shown.

Still referring to FIG. 7, the transflective LCD 700 further includes ahigh efficiency backlight cell assembly 420. Backlight assembly 420preferably contains one or two orthogonal sheets of brightnessenhancement films and other multiple polymeric films for enhancingtransmission and optical performances. However, any conventionalbacklight cell or high bright backlight cell, with edge lamps orbackside lamps, can be used.

Commercial TFT LCDs of various sizes and structures can easily bemodified in accordance with the teachings of the present invention togenerate LCDs viewable under direct sunlight. Optimal viewingperformances are obtained by adjusting proper orientations of thediffusing element and the reflective polarizer according to thepolarization transmission characteristics of the existing liquid crystaldisplay panel. The following examples illustrate how differentcommercial TFT LCDs can be modified in accordance with the teachings ofthe present invention to generate transflective LCDs.

EXAMPLE 1

A Direct Sunlight Readable 15″ TFT LCD

Referring now to FIG. 8, a diagram of the structure of a 15″ desktopmonitor Thin Film Transistor Liquid Crystal Display (TFT LCD) is shown(related art). The LCD 800 comprises a display unit 801 with a liquidcrystal panel sandwiched between a pair of dichroic polarizers. Thedichroic polarizers have off-axis transmission directions. The backlightcell 810 includes a diffusive reflector 805, a wave guide plate withfour lamps 804, a rear diffuser 803 positioned in front of wave guideplate 804, a sheet of brightness enhancement film 802 positioned in thefront side of rear diffuser 803 and a front diffuser 806 positioned infront of the brightness enhancement film 802. The TFT LCD illuminatesabout 250 to 275 nits. The display performs nicely indoors butvisibility diminishes when the display moves outdoors. The image istotally invisible when the display is positioned towards directsunlight.

With reference to FIG. 9, a diagram of an embodiment of the presentinvention modifying the 15″ desktop monitor TFT LCD 800 is shown. Thetransflective TFT LCD 900 constructed in accordance to the presentinvention includes the major components of the low reflection liquidcrystal display unit 920, the diffusing transflector 930, and the highefficient backlight cell 910. Applying an anti-reflection coating 901 onthe front surface of 801 generates the low reflection display unit 920,preferably with less than 15% haze and an anti-reflection efficiencyless than 1%. The anti-reflection coating 1801 is a plastic film boundto the front surface 1701. The diffusing transflector 930 comprises asheet of diffuser, 902, and a diffuser laminated selective reflectivepolarizer 903. This diffusing transflector 930 is positioned on the rearside of the display unit 920 in accordance to the teaching of thepresent invention. The transflective LCD 900 has an enhancedtransmissive illumination between 350 and 400 nits. Indoor and outdoorperformance is greatly enhanced without altering the viewing angle orresolution. Under direct sunlight, the transflective illuminationeffectively dominates the lighting of the display and renders thedisplay images viewable.

Referring now to FIG. 10, a diagram of a comparison of temperaturemeasurements between the regular LCD 800 and the modified LCD 900 isshown. Thermal couples are adhered to the center of the rear side of thedisplay units in 800 and 900, as shown by 850 and 950 in FIG. 8 and FIG.9, respectively. The displays were provided with the same operatingconditions and voltage supplies. Curve 1003 shows the outdoor airtemperatures ranging from 30° C. to 40° C. Curve 1001 shows thetemperature measurements of the transflective LCD 900, and curve 1002shows the temperature measurements of the regular LCD 800. Both regularLCD 800 and transflective LCD 900 reach an equilibrium operatingtemperature between 76° C. and 78° C. The transflective LCD 900 does notgenerate any excessive heat in the system when compared to the regularLCD 800.

EXAMPLE 2

A Direct Sunlight Readable 14.2″ Notebook Computer TFT LCD

With reference to FIG. 11, a diagram of the structure of a 14.2″notebook computer TFT LCD is shown (related art). The LCD 1100 comprisesa display unit 1101 with a liquid crystal panel sandwiched between apair of dichroic polarizers with parallel transmission directions. Thebacklight cell 1110 is composed of a diffusely reflector 1105, a waveguide plate coupled with one lamp 1104, a sheet of diffuser 1103positioned on the front side of wave guide plate 1104, two sheets ofbrightness enhancement film 1102 positioned in the front side ofdiffuser 1103, and another diffuser 1106 in front of enhancement film1102. The above described unit illuminates between 120 and 140 nits. Thedisplay performs well indoors but is very difficult to view under anyoutdoors conditions.

Referring now to FIG. 12, a diagram of an embodiment of the presentinvention modifying the 14.2″ notebook computer TFT LCD 1100 is shown.The transflective TFT LCD 1200 comprises the major components of the lowreflection liquid crystal display unit 1220, the diffusing transflector1230, and the high efficient backlight cell 1210. Applying ananti-reflection coating 1201 on the front surface of 1101 generates thelow reflection liquid crystal display unit 1220, preferably with lessthan 15% haze and an anti-reflection efficiency less than 1%. Theanti-reflection coating 1801 is a plastic film bound to the frontsurface 1701. The diffusing transflector 1230 is composed of one sheetof diffuser 1202 and a reflective polarizer 1203. This diffusingtransflector 1230 is positioned on the rear side of the display unit1220 in accordance to the teaching of the present invention. Thetransflective LCD 1200 has an enhanced transmissive illumination ofbetween 175 and 185 nits, yielding better indoor performances. Inaddition, the display is visible under all outdoor lighting conditionsincluding direct sunlight regardless of its transmissive illumination.

EXAMPLE 3

A Direct Sunlight Readable 10.4″ Tablet TFT LCD

With reference to FIG. 13, a diagram of the structure of a 10.4″ TabletTFT LCD is shown (related art). The LCD 1300 comprises a display unit1301 with a liquid crystal panel sandwiched between a pair of dichroicpolarizers with parallel transmission directions. The backlight cell1310 is composed of a diffusive reflector 1305, a wave guide platecoupled with one edge lamp 1304, a sheet of diffuser 1303 positioned inthe front side of wave guide plate 1304, a sheet of brightnessenhancement film 1302 positioned in front of diffuser 1303, and areflective polarizer 1306 in front of enhancement film 1302. The abovedescribed unit illuminates approximately 200 nits. The display givesgood optical performances indoors, yet is very difficult to view underany outdoor conditions.

With reference to FIG. 14, a diagram of an embodiment of the presentinvention modifying the 10.4″ Tablet TFT LCD 1300 is shown. Thetransflective TFT LCD 1400 includes the major components of the lowreflection liquid crystal display unit 1420, the diffusing transflector1430, and the high efficient backlight cell 1410. Applying ananti-reflection coating 1401 on the front surface of 1301 generates thelow reflection liquid crystal display unit 1420, preferably with lessthan 15% haze and an anti-reflection efficiency less than 1%. Theanti-reflection coating 1401 is a plastic film bound to the frontsurface 1301. The diffusing transflector 1430 is composed of one sheetof diffuser 1402 and a reflective polarizer 1306. The diffusingtransflector 1430 is positioned on the rear side of the display unit1420 in accordance to the teaching in the present invention. Thetransflective LCD 1400 has about the same transmissive illumination asLCD 1300 and is visible under all outdoor lighting conditions, includingdirect sunlight.

EXAMPLE 4

A Direct Sunlight Readable Open Frame 12.1″ TFT LCD

With reference to FIG. 15, a diagram of the structure of a 12.1″ openframe high bright TFT LCD is shown (related art). The LCD 1500 comprisesa display unit 1501 with a liquid crystal panel sandwiched between apair of dichroic polarizers with off-axis transmission directions. Thebacklight cell 1510 comprises a diffusive reflector 1505, a wave guideplate with ten back side lamps 1504, a sheet of diffuser 1503 positionedin the front side of wave guide plate 1504, a sheet of brightnessenhancement film 1502 positioned in front of diffuser 1503, and anotherdiffuser 1506 in front of enhancement film 1502. The above-describedunit illuminates approximately 700 to 800 nits. The display gives verygood optical performances indoor with partial transmission illumination.With full transmission illumination (i.e. 800 nits), the displayprovides good visibilities under moderate ambient light. However, thedisplay generates excessive heat and therefore reaches its clearingtemperature in approximately 30 minutes, a short amount of time. Uponreaching its clearing temperature, the display turns black. Under verystrong ambient light or direct sunlight, the display is difficult toview even when provided with full transmission illumination provided byits backlight.

With reference to FIG. 16, a diagram of an embodiment of the presentinvention modifying the 12.1″ open frame high bright TFT LCD 1500 isshown. The transflective TFT LCD 1600 comprises the major components ofthe low reflection liquid crystal display unit 1620, the diffusingtransflector 1630, and the high efficient backlight cell 1610. Applyingan anti-reflection coating 1601 on the front surface of 1501 generatesthe low reflection liquid crystal display unit 1620, preferably withless than 15% haze and an anti-reflection efficiency less than 1%. Theanti-reflection coating 1601 is a plastic film bound to the frontsurface 1501. The diffusing transflector 1630 is composed of one sheetof diffuser 1602 and a reflective polarizer 1603. This diffusingtransflector 1630 is positioned on the rear side of the display unit1620 in accordance to the teaching of the present invention. Thetransflective LCD 1600 has approximately the same transmissiveillumination as 1500, yielding the same satisfactory indoorperformances. Unlike TFT LCD 1500, however, transflective TFT LCD 1600is visible under all outdoor lighting conditions, including directsunlight, regardless of the amount of transmissive illumination.

EXAMPLE 5

A Direct Sunlight Readable 1.5″ TFT LCD

With reference to FIG. 17, a diagram of the structure of a 1.5″ TFT LCDis shown (related art). A 1.5″ TFT LCD is commonly used as a monitor ona digital camera. The LCD 1700 comprises a display unit 1701 with aliquid crystal cell, a first dichroic polarizer, and a circularpolarization-generating element (not shown). The backlight cell 1710comprises a diffusely reflector 1705, a wave guide plate with four edgeLED 1704, a sheet of diffuser 1703 positioned in the front side of waveguide plate 1705, two sheets of brightness enhancement film 1702 and1707 positioned in front of diffuser 1703, and another diffuser 1706 infront of the brightness enhancement film sheets 1702 and 1707. Theabove-described unit illuminates approximately 150 to 200 nits in thecamera system. The display gives moderate optical performances indoor,and is very difficult to view under any outdoor conditions.

With reference to FIG. 18, a diagram of an embodiment of the presentinvention modifying the 1.5″ TFT LCD 1700 is shown. The transflectiveTFT LCD 1800 comprises the major components of the low reflection liquidcrystal display unit 1820, the diffusing transflector 1830, and the highefficient backlight cell 1810. Applying an anti-reflection coating 1801on the front surface of 1701 generates the low reflection liquid crystaldisplay unit 1820, preferably with less than 15% haze and ananti-reflection efficiency less than 1%. The anti-reflection coating1801 is a plastic film bound to the front surface 1701. A quarter waveplate 1804 is positioned on the rear of the display unit 1820 togenerate a linear polarization from the circular polarization output ofthe display unit 1820. The second dichroic polarizer 1805 is then placedat the rear side of the quarter wave plate 1804. The transmissiondirection for the second dichroic polarizer 1805 is parallel to thedirection of the linear polarization output of the quarter wave plate1804. The diffusing transflector 1830 is composed of one sheet ofdiffuser 1802 and a reflective polarizer 1803. This diffusingtransflector 1830 is positioned on the rear side of the dichroicpolarizer 1805 in accordance to the teaching in the present invention.The transflective LCD 1800 has less transmission illumination than TFTLCD 1700, with values between 100 nits and 150 nits. However, thedisplay 1800 is more visible under all lighting conditions, includingdirect sunlight, due to its transflective property and enhancedcontrast.

In summary, the present invention resolves and considers the reflectionand transmission properties of the transflector to provide atransflective LCD with optical properties tailored for indoor andoutdoor applications. A high efficiency multi-layer anti-reflectioncoating (AR coating) not only reduces the background reflection of theLCD front surface, but also allows the liquid crystal display unit totransmit more energy of incident light, thus providing more reflectiveillumination. Before, incident light was partially reflected on thesurface of the substrate. With the present invention, the low reflectionand high transmission properties of the AR coating and the diffusingtransflector cooperatively provide the display with optimalilluminations.

Other embodiments of the invention will appear to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples to be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

1. A method of making an LCD viewable under all lighting condition froman LCD having a liquid crystal cell positioned between a first dichroicpolarizer and a second dichroic polarizer, and a backlight assemblypositioned behind the second dichroic polarizer, the method comprisingthe steps of: (a) positioning an anti-reflection layer with a surface ofhaze value less than 15% in front of the first dichroic polarizer; and(b) positioning a diffusing transflector between the backlight assemblyand the second dichroic polarizer, the diffusing transflector comprisinga diffusing element and a reflective polarizer, the diffusing elementbeing a transparent substrate layer or a corrugated surface having ahaze value of 10% to 85%, and the reflective polarizer being positionedwith its transmission direction forming an angle of 0 degree, between 0and 60 degrees, or between −60 and 0 degrees to the transmissiondirection of the second dichroic polarizer.
 2. A method of making an LCDviewable under all lighting condition from an LCD having a liquidcrystal cell positioned between a first dichroic polarizer and a seconddichroic polarizer, a backlight assembly positioned behind the seconddichroic polarizer, and a reflective polarizer positioned between thebacklight assembly and the second dichroic polarizer with itstransmission direction forming an angle of 0 degree, between 0 and 60degrees, or between −60 and 0 degrees to the transmission direction ofthe second dichroic polarizer, the method comprising the steps of: (a)positioning an anti-reflection layer with a surface of haze value lessthan 15% in front of the first dichroic polarizer; and (b) positioning adiffusing element between the second dichroic polarizer and thereflective polarizer, the diffusing element being a transparentsubstrate layer or a corrugated surface having a haze value of 10% to85%.
 3. A method of making an LCD viewable under all lighting conditionfrom an LCD having a liquid crystal cell positioned between a firstdichroic polarizer and a second dichroic polarizer, a backlight assemblypositioned behind the second dichroic polarizer, and a diffusingtransflector positioned between the backlight assembly and the seconddichroic polarizer, the diffusing transflector comprising a diffusingelement and a reflective polarizer, the diffusing element being atransparent substrate layer or a corrugated surface having a haze valueof 10% to 85%, and the reflective polarizer having its transmissiondirection forming an angle of 0 degree, between 0 and 60 degrees, orbetween −60 and 0 degrees to the transmission direction of the seconddichroic polarizer, the method comprising the step of positioning ananti-reflection layer with a surface of haze value less than 15% infront of the first dichroic polarizer.
 4. A method of making an LCDviewable under all lighting condition from an LCD having a liquidcrystal cell positioned between a first dichroic polarizer withanti-reflection treatment and surface haze less than 15% and a seconddichroic polarizer, a backlight assembly positioned behind the seconddichroic polarizer, the method comprising the step of: positioning adiffusing transflector between the backlight assembly and the seconddichroic polarizer, the diffusing transflector comprising a diffusingelement and a reflective polarizer, the diffusing element being atransparent substrate layer or a corrugated surface having a haze valueof 10% to 85%, and the reflective polarizer being positioned with itstransmission direction forming an angle of 0 degree, between 0 and 60degrees, or between −60 and 0 degrees to the transmission direction ofthe second dichroic polarizer.
 5. A method of making an LCD viewableunder all lighting condition from an LCD having a liquid crystal cellpositioned between a first dichroic polarizer and a second dichroicpolarizer, a backlight assembly positioned behind the second dichroic,polarizer, and a diffusing element being a transparent substrate layeror a corrugated surface having a haze value of 10% to 85% in front ofthe backlight assembly, the method comprising the steps of: (a)positioning an anti-reflection layer with a surface of haze value lessthan 15% in front of the first dichroic polarizer; and (b) positioning atransflector between the backlight assembly and the diffusing element,the transflector being a reflective polarizer positioned such that itstransmission direction forms an angle of 0 degree, between 0 and 60degrees, or between −60 and 0 degrees to the transmission direction ofthe second dichroic polarizer.
 6. A method of making an LCD viewableunder all lighting condition from an LCD having a liquid crystal cellpositioned between a first dichroic polarizer with anti-reflectiontreatment and surface haze less than 15% and a second dichroicpolarizer, a backlight assembly positioned behind the second dichroicpolarizer, and a reflective polarizer positioned between the seconddichroic polarizer and the backlight assembly with its transmissiondirection forming an angle of 0 degree, between 0 and 60 degrees, orbetween −60 and 0 degrees to the transmission direction of the seconddichroic polarizer, the method comprising the step of: positioning adiffusing element between the second dichroic polarizer and thereflective polarizer, the diffusing element being a transparentsubstrate layer or a corrugated surface having a haze value of 10% to85%.